1. Field of the Invention
The present invention relates to a motor drive device for driving an electric motor.
2. Description of Related Art
The structure of a conventional electric blower, for a vehicle seat air-conditioning device, will be schematically described with reference to FIG. 5.
The electric blower includes a brushless motor 1, and a vane wheel 5 fixed to an output shaft 1a of the brushless motor 1. The brushless motor 1 includes a rotor 3 fixed to the output shaft 1a, a stator 2 arranged on the inside of the rotor 3, and a bearing 4 for rotatably supporting the output shaft 1a. The bearing 4 consists of an inner ring 4a fixed to the output shaft 1a, an outer ring 4b fixed to a yoke 2a of the stator 2 and balls 4c interposed between the inner ring 4a and the outer ring 4b. 
The electric blower is incorporated in the back of a seat or in a seat cushion. The electric blower can vibrate when the vehicle traveles on a rough road such as a gravel road. The inner ring 4a, outer ring 4b and balls 4c in the bearing 4 vibrate when the electric blower vibrates.
When the electric blower is stopped, there is no change in the contact positions of the outer ring 4b, balls 4c and inner ring 4a. Therefore, if the electric blower vibrates many times when the electric blower stops, the contact positions are damaged. As a result, the bearing 4 is damaged and may generate abnormal noises.
Therefore, to absorb vibration and protect the bearing, a vibration-absorbing material such as an urethane material is arranged between the electric blower and the seat.
The seat air-conditioning device for a vehicle described above, however, is more costly due to the use of the vibration-absorbing material to absorb the vibration of the electric blower.